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SIMPLY SCIENCE: Even gobblers get the blues

There are a lot of depressed turkeys these days. It’s not hard to tell a depressed turkey from one that’s in good spirits.

Depressed birds stand with their heads tilted downward or drawn into their body. Their feathers are ruffled, and their wings droop. Their eyes are partly closed. The birds may act alert and agitated when disturbed, but they quickly become lethargic again.

By comparison, normal turkeys are highly excitable and often seen strutting around as if they had good sense, which they don’t.

It’s hard to determine the cause of turkey depression. It’s not that they don’t have adequate reasons for being depressed. More than 140 million of them die each year in the United States alone. Even if they themselves don’t meet an untimely fate, they have undoubtedly lost friends and relatives, or soon will. But it is a far more complex matter than it first appears.

Turkey depression seems to run highest in urban-turkey settings such as turkey farms and large cities, where feelings of isolation, in the midst of crowds, are a common phenomenon. In addition, crowding seems to bring out unusual behaviors in turkeys, including alienation from authority, violence, mob rule, sexual deviation and public health risks that contribute to poor mental health. Feelings of dependency and worthlessness aggravate the condition.

A number of names have been proposed to describe the condition that is turkey depression: turkey blues, occupiensis or blackhead, are common. But as with humans, the causes of turkey depression are several and careful diagnosis is required.

Actually there are three distinct conditions that scientists have categorized. The first, “turkey blues” may be nothing more than serotonin imbalance. The timing is highly seasonal and may be related to day length, a condition commonly called Seasonal Affective Disorder (SAD). The second condition, known as occupiensis, may affect as much as 99 percent of the turkey population. The severity of symptoms these turkeys exhibit apparently varies exceedingly.

Blackhead, on the other hand, is an actual disease that is well-known among turkeys and other bird brains. It is caused by a parasite called Histomonas meleagridis.

This single-celled parasite affects several bird species, but it seems to be most severe in turkeys. It is also known as infectious enterohepatitis, or histomoniasis. The parasite inhabits the bird’s intestinal tract but also invades the liver. In both places it causes extensive tissue degradation. That’s what is so depressing.

Adding insult to injury, Histomonas is transmitted between turkeys by another parasite, Heterakis gallinarum, which is an intestinal worm of turkeys. So ... the parasite of turkeys is transmitted to turkeys by parasitizing a parasite of turkeys. This is reminiscent of the old nursery rhyme:

Big fleas have little fleas Upon their backs to bite ‘em. And little fleas have lesser fleas, And so, ad infinitum.

The Blackhead organism cannot survive outside the turkey very long, but it can become encapsulated in the egg of the Heterakis worm. The egg of the worm can then survive for many weeks, depending on environmental conditions.

Turkeys with advanced Blackhead develop a sulfuric diarrhea that spreads to the eggs, and Histomonas, over a wide area. Another slight twist to the whole situation is that earthworms often ingest the Heterakis eggs and carry them deeper into the soil. Here the parasite survives longer and is spread out over an even larger area.

Make no mistake, though. Turkey depression costs you a lot of money. Mortality from turkey depression can be as high as 80 to 90 percent, and surviving turkeys are seldom worth much. The cost of depressed turkeys must be compensated for by the price of surviving turkeys. Consequently, depressed turkeys cost us money.

Oh, and the increased cost for the un-depressed turkeys leads to even more depression, at least among turkey consumers. This year there seems to be more than the normal number of depressed turkeys out there.

It’s very depressing.

Gary McCallister is professor of biology at Colorado Mesa University and just found out he won an award for humorous column writing through the Colorado Press Association.